Democrat Jake Auchincloss, seeking Fourth District seat, was a registered Republican in 2014

Jake Auchincloss.Rick Bern/Handout

As a Democrat running for Congress, Jake Auchincloss has touted “progressive” transportation policies. He’s pointed to his endorsement by Progressive Newton when he ran for City Council. On his proposals to curb gun violence, he says “there is no one to the left of me.”

Less often he’s discussed his brief time on the right of the Massachusetts political spectrum. Auchincloss, now running in the Fourth District’s Democratic primary, was a registered Republican in late 2013 and 2014, a stretch in which he held a paid position helping get Charlie Baker elected governor, according to records and his campaign.

The job, Auchincloss said, was focused on organizing and voter mobilization for Baker’s campaign when he ran in the open gubernatorial race that eventually pitted him against Democratic nominee Martha Coakley. A registered Democrat originally, Auchincloss changed parties in late 2013, according to records from the Newton clerk’s office, before unenrolling from the Republican Party in April 2014.

Auchincloss then voted in the Republican primary that fall before enrolling again with the Democratic Party in November 2015, days after first winning election to what was then Newton’s Board of Aldermen. In Massachusetts, independent voters are allowed to select in which primary they cast a ballot.

Auchincloss, a 32-year-old Newton city councilor and Marine corps veteran, defended his Democratic credentials, which include pulling Democratic ballots in every presidential primary since 2008 and in the 2018 state Democratic primary, records show. He said he switched parties in late 2013 because “he wanted to support [Baker] in his primary challenge" against Mark Fisher, a Tea Party-aligned Republican whom Baker ultimately beat by nearly 50 points in the September primary the next year.

That Auchincloss-backed Baker, a socially liberal Republican, isn’t necessarily at odds with other Democrats, who polls show have given the governor higher approval ratings than those within his own party.

But his history, including his work on Baker’s campaign, could complicate his path among liberal voters weighing choices in a nine-person primary, where other contenders have tried to carve out progressive ground.

Records submitted by local officials to a state database indicate none of the other primary candidates had previously registered as Republican, though some had been independent voters before enrolling as Democrats.

“I did not agree with Governor Baker on everything,” said Auchincloss, who interned in Governor Deval Patrick’s office while in college. “I felt that Governor Baker was the right leader for the moment and that he would be a competent leader for Massachusetts.”

Auchincloss said his core beliefs didn’t change, and his record has a “consistent thread" of supporting immigration reform, gun safety, and abortion rights in his time on the Newton City Council, where he’s since been reelected twice.

“I am a Democrat,” he said. “I supported Democrats up and down in the ballot consistently throughout my career.”

Pressed on how he voted in the 2018 general election, Auchincloss said he again voted for Baker, who won by 33 percentage points over Democratic nominee Jay Gonzalez.